programming-for-dummies

242
Polymorphism: Modifying Code without Changing Its Name
By keeping the amount of code stored inside each object to a minimum,
object-oriented programming makes it easy to understand how each object
works. Through inheritance, OOP makes it easy to update one subprogram
that’s reused in other objects.
As a result, inheritance makes reusing objects (and their subprograms) practical
and modifying those objects’ subprograms fast, simple, and easy.
Inheritance offers the convenience of reusing code without the inconvenience
of updating that code in multiple locations.
Polymorphism: Modifying Code
without Changing Its Name
Besides reusing existing subprograms (without modifying them) and adding
new subprograms to an object, you can also modify an inherited subprogram
through polymorphism.
Polymorphism lets you inherit a subprogram from another object and then
replace the code in that subprogram with brand new code. So essentially all
you’re really reusing is the original subprogram’s name, as shown in Figure 7-9.
Object A
Subprogram Move
Code 1
Code 2
Figure 7-9:
Polymorphism
lets you
reuse a
subprogram
name in
another
object.
Object B
Subprogram Move
Code 30
Code 31
Code 32
The purpose of polymorphism is to let multiple objects use the same
descriptive subprogram name. Normally, two subprograms can’t share the
same name. Otherwise, when you call a subprogram by name, the computer
doesn’t know which subprogram you actually want to use.